f 
208 CHEMICAL MANUFACTURES IN GLASGOW, ETC. 
of water. This method was not economical. A portion of 
the sulphur would unite with the potash of the saltpetre, 
and form with it a sulphuret, and probably a portion of the 
sulphuric acid formed, would also unite with the potash and 
form a sulphate. When Messrs. Knox, Tennant, and Macin- 
tosh established their works at St. Rollox, they separated the 
sulphur from the saltpetre ; the sulphur was burnt over a 
stove, and an iron cup, containing the requisite quantity of 
saltpetre, was placed over the burning sulphur. 
By this contrivance the sulphur was completely converted 
into sulphurous acid, and the whole of the nitric acid crrried 
along with it into the leaden chambers. The size of the leaden 
chambers was gradually increased, and the substitution of 
steam for water formerly placed at the bottom of the chambers 
was a vast improvement. The acid which collects at the bot- 
tom of the chambers has a specific gravity of 1.75, or it is a 
compound of one atom anhydrous acid, and two atoms water. 
This acid is concentrated by heating it in a platinum still, till 
the second atom of water is driven off. When this manufac- 
ture is at full work, the quantity of sulphuric acid made in it 
exceeds 300,000lbs avoirdupois, per week. When he first 
began to purchase acid, about forty-five years ago, it cost 8d. 
per pound ; the present price is under a penny a pound. 
3. One of the great purposes to which sulphuric acid is ap- 
plied at St. Rollox's, is the manufacture of bleaching powder, 
or chloride of lime, as it is now called. When the mode of 
bleaching by chlorine was introduced into Great Britain, by 
Mr. Watt, in 17S7, the very offensive smell and deleterious 
effects of the gas upon the workmen, was a formidable obsta- 
cle to its use. Various methods were tried to remove this 
objection. It was found that if potash, or soda was dissolved 
in the water before it was impregnated with the chlorine gas, 
the disagreeable smell was destroyed ; but unfortunately the 
addition destroyed, at the same time, the bleaching power of 
the gas. At last Messrs. Knox, Tennant, and Macintosh dis- 
covered that if lime was mixed with the water, before it was 
mixed with the gas, the disagreeable smell was obviated, 
